SQLite basic -4. Data Definition Language (DDL)

First, create a database

1. Create a way

In the second chapter we saw how to use PyCharm create SQLite database. For details, see Bowen
use this method to create the database: flask_dev

2. The database naming convention

Uses 26 letters of the alphabet (case-sensitive) and natural numbers (often do not need) 0-9 plus underscore ' ' composed, clear and concise name, multiple words are underlined ' ' separated by a project database, a number of projects carefully use the same database

Second, create a table

Creating tables, comes to naming table, column and data type definitions for each column.

1. Basic Usage

-- 语法
CREATE TABLE database_name.table_name (
    column1 datatype PRIMARY KEY,
    ...
    columnN datatype,
);

-- 实例
CREATE TABLE flask_dev.link_men (
    ID INT PRIMARY KEY NOT NULL,
    NAME          TEXT NOT NULL,
    BIRTHDAY  DATETIME NOT NULL,
    ADDRESS   CHAR(50),
    SALARY    REAL,
);

Table 2. Data naming

1. 26 using letters (case sensitive) and a natural number (often not required), plus 0-9 underscore ' ' composition, clear and simple name, a plurality of words are underlined ' ' separated
2. All lowercase names, banned capital
3. Prohibit the use of the database keyword, such as: name, time, datetime, password, etc.
4. Table name should not be made too long (usually no more than three English words)
5. Name of the table is generally a noun or verb-object phrase
6. It represents the name of the singular, for example, Employee, instead of employees
7. The table must fill out a description (when using SQL statements to build the table)

Name list is as follows: name of the main character table + dtl (detail abbreviation)
such as: name purchase order is: po_order, the purchase order list is: po_orderdtl

Follow the following principles:

Module function points ① + _ Example: alllive_log alllive_category
② Function Point Example: Message Live
③ represents a general embodiment: all_user

3. The field naming convention

1. 26 using letters (case sensitive) and a natural number (often not required), plus 0-9 underscore ' ' composition, clear and simple name, a plurality of words are underlined ' ' separated
2. All lowercase names, banned capital
3. Descriptive information fields must be filled
4. Prohibit the use of the database keyword, such as: name, time, datetime password, etc.
5. Field name commonly used noun or verb-object phrase
6. It takes the name field must be easy to understand, generally no more than three English words
7. When naming the list, do not repeat the name of the table
8. Do not include data type in the name of the column
9. Field is named using the full name, abbreviation ban

For example, avoid using field called employee_lastname in the name of the employe table
follow the following principles:

① noun Example: user_id user_name Sex
② verb-object example phrase: is_friend is_good

Third, delete the table

To remove table definition and all data, indexes, triggers, constraints, and permission specifications of the table.

Once a table is deleted, all the information in the table will be lost forever.

-- 语法
DROP TABLE dababase_name.table_name;

-- 实例
DROP TABLE flask_dev.link_men;